Coupling system



N. P. cAsE COUPLING SYSTEM Filed June 21, 1935 May 18', 1937.

ATTORNEY.

Patented May 18,1937

UNITED STATE COUPLING SYSTEM Nelson P. Case, Bayside, N. Y., asaignor to Baleitine Corporation, a corporation of Delaware Application June 21, 1935, serial No. 27,050A

12 Claims.

there is also obtained an antenna to detectorl over-all gain which is greater than is needed or desired. It is therefore desirable to provide, under such conditions, means that will alter the over-all gain without impairment of the selectlvity and fidelity of the receiver.

The above problem becomes more acute in multiband radio receivers, for a general characteristic of such receivers is that the attainable antenna to detector over-all gain is smaller as the band in which the receiver is tunable is higher in the frequency spectrum. As a conse-y f quence, in multi-band radio receivers there is the. further problem of providing means which compensates for such variations in gain so as to obtain an over-all gain which is more nearly uniform from band to band. v

It is an object of this invention coupling system by lmeans of which the over-al1 gain of a radio receiver may be altered or controlled in al simple, economical manner without impairment of the selectivity or dellty of the receiver. y

It is another object 4of the invention to provide a coupling system for. multi-band radio receivers which is effective automatically to control the l over-all gain in accordance with the band in vwhich the receiver is operated, such coupling sys-y 40 tem being of simple and economical construction and eifectlve without impairment of the4 selectivity and delity of the receiver.

A further object of the invention is the provision of a coupling system employing high inducr tances and in which the inductance elements may be constructed and mounted in the receiver with ease and economy. f

Other objects of this invention will become apparent from the specication taken in conjunction withv the accompanying drawing and the ap# pended claims.' Y y The principal held of use of this invention is as a coupling system between successive radio- 55 frequency stages of a radio receiver.

yto provide a i The invention contemplates, for a given band of frequencies, a coupling system comprising -a fixed tuned primary circuit and a secondary circuit. The primary erably tuned to a fixed frequency variably tuned circuit is prefsomewhat below the lowest frequency ofthe given band, with the secondary circuit tunable over the given band,

preferably by a variable condenser. In accordance with this invention, the secondary circuit is non-inductively related to the primary circuit, the coupling between the two circuits being provid` ed by a capacitance .of such value. that it serves also to align the secondary circuit with one or more other associated tunable circuits.

Since,

in accordance with the invention, the primary and secondary circuits are non-inductively related, the primary circuit inductanc ondary circuit inductance may be,

e and the secand preferably are, mounted independently. This contributes to the simplicity of the receiver const ruction, for the primary circuit inductance is relatively large and the mounting of it in inductive relation with the secondary circuit inductance involves various mechanical expedients in manufacture and assem- 0 bly, all of which entail expense. This expense is avoided with this invention.

The invention contemplates, fo

r two or more bands of frequencies, a coupling system for each one band, with band similar to that described for the provision that the coupling capacitances for the several bands progressively increase in valuev v as the respective bands are higher in the f requency spectrum. It is also a provision of the invention that the ratio of the maximum to minimum frequencies in the several bands decrease as the bands are higher in the frequency spectrum. The single figure of the drawing is a circuit diagram, partly schematic, illustrating an embodiment 'of the invention as incorporated in a' multi-band superheterodyne receiver.

Referring now to the drawing, the multi-band superheterodyne receiver rthere shown comprises an antenna circuit lll' connected to a radio-fre.-

quency selector circuit il.

The selector circuit signal frequencies.

circuit il is connected to the signal input circuit of vacuum tube il, operating as a r amplifier.

adio-frequency The output of the selector The output circuit of vacuum tube I4 is cona constant intermediate or beat frequency in the output of the oscillator-modulator I1. The oscillator-modulator I1 is connected in cascade with an intermediate-frequency amplifier 22, a detector and automatic gain control source 23, anv audio-frequency amplifier 24, and a sound reproducer 25. The automatic gain control biaspotential may be applied to one or more of the intermediate-frequency amplifier 22, the oscillator-modulator I1 and the radio-frequency amp'lifler^ tube I4, as desired. Switch I2 of the radio-frequency selector circuit II and switch 20 of the oscillator-modulator I-l are preferably ganged for unicontrol, as indicated by the dotted lines 26. Also ganged with switches I2 and 20 are four switches 21, 28, 29, and 30 of the coupling system I6, as will be described hereinafter.

The variable tuning condenserl of the radiofrequency selector circuit II and the variable condenser 2| of the oscillator-modulator II are preferably ganged for unicontrol, as indicated by the dotted lines 33. A variable tuning condenser 34 for coupling system Il, in general similar to variable condensers I3 and 2i, is also' ganged with these variable condensers, as will be described hereinafter. i

Considering rst the operation of the receiver as a whole, and neglecting for the moment the coupling system I3.' per se, the desired received signal wave is selected in selector circuit II, amplied in tube I4, further selected and transferred by coupling system I5 to the oscillator modulator I1, where the signal is converted into a signal-modulated intermediate frequency. 'I'he signal, as thus converted, is amplified in the intermediate-frequency amplifier 22, converted by detector 23 into the audio frequencies of modulation, amplified in the audio-frequency amplifier 24, and reproduced 'by the sound reproducer 25.

The amplification of the received signal is subject to automatic control by the 'A. V. C. bias potentials, according to the manner well understood in the art.

The coupling s'ystem generally designated I6, comprises a pluralityof primary circuits, generally designated 35, a plurality of secondary circuits, generally designated 36, and a plurality of capacitive couplings, generally designated 31,- one of each for each of the different bands over which the receiver is tunable. While the circuits 35 and 35 have been referred to as "primary and secondary circuits, respectively, for the sake of convenienc'efit is to be expressly understood tomarily the. general broadcast band, ranging approximately from 500 to 1500 kilocycles) includes a winding 45a,-usually of relatively high y,

inductance, connected in the plate circuit of vacuum tube I4 when the arm. of switch 21 is in engagement with contact 4Ia, one terminal of winding 43a being eifectively grounded through condenser 39. The secondary circuit 36 for such lowest band of frequencies includes a winding 42a, usually of relatively low inductance, noninductively related to the winding 40a and connected to the signal input circuit 43, 46 of oscillator-modulatorl I1 through a condenser 45, when the arm of switch-28 is in engagement with contact 44a. The secondary circuit 36 for such lowest band of frequencies also includes the variable tuning condenser 34, one terminal of which is grounded.

Primary circuit inductance 40a and secondary circuit inductance 42a being non-inductively related, are conveniently, land preferably, separately mounted. As illustrated, winding 40a is mounted within a grounded shield can 41, and winding 42a is mounted within another grounded shield can 43. l

The capacitive coupling 3l for the lowest band of frequencies,' comprises a small adjustablyfixed capacitance 31a interconnecting high potential portions of the primary and secondary circuits, preferably the high potential terminals of windings 40a and 42a.

The primary circuit 35 forthe lowest band of frequencies is preferably ilxedly tuned to a. frequency somewhat below the lowest frequency of such band by capacitance in shunt with winding 40a.v This capacitance may comprise a separate condenser orv the inherent capacitance of the primary circuit, such as the output capacitance of the vacuum tube I4, including the capacitance due to the presence of the shield customarily provided around the vacuum tube I4, the capacitance to ground of the primary circuit connections, and the distributed capacitance of the winding 40a. This inherent capacitance of the primary circuit is for convenience designated 5I and represented in the drawing, in dotted lines, as a single equivalent fixed capacitance connected between the plate of vacuum tube I4 and ground.

The secondary circuit 33 for the lowest band of frequencies-such circuit including, in series, the winding 42a, variable tuning lcondenser 34 and fixed condenser 45-is tunable by variable condenser 34 over a-band which has a fixed relationship to the tuning bands of the corresponding radiofrequency selector circuit and the corresponding oscillation circuit. Adjustably-iixed condenser 31a is of -such value, together with.the inherent capacitance 5I of the primary circuit 35, as to align the secondary circuit 36 with the radio-frequency selector circuit II and the oscillation circuit of the oscillator-modulator Il over their respective bands. Such alignment of secondary circuit 36 by adjustably-fixed condenser 3`Ia has its principal effect in the highfrequency portion of such band,l similar to the well-known eiiect of a parallel trimming capacitance.- Fixed condenser 45 serves in the conventional manner to align the secondary circuit with thel other tunable circuits in the low-frequency portion of such band and also to by-pass radiofrequency currents aroundthe A. V. C. resistors.

It will thus be seen that adiustably-xed condenser 31a ser'ves, for the lowest frequency band over which the receiver is tunable, not only as the coupling means between the primary and secondary circuits, 35 and 33 for such band, but also to tween primary and secondary circuits and 36 is relatively small, thus providing a coupling sys- -tem that has an over-all transfer ratio somewhat less than that of conventional coupling systems. At the same time, the progressive decrease in the capacitive reactance of condenser 31d, and the f consequent progressive increase in the capacitive coupling between the circuits 35 and 36, as the system is tuned to the higher frequencies of any particular band, compensates for the progressive decrease in the responsiveness of the primary cir cuit 35, due to` that fact that it is permanently Atuned somewhat below the band.

Thus, coupling system I6 comprises an interstage radio-frequency coupling system constituting a simple, effective 'and economical gain proportioning or reducing means that does not impair the selectivity or fidelity of the receiver.

' For each of 4the other bands of frequencies to which the receiver is tunable there is a primary circuit inductance mounted within the shield can 41, a secondary circuit inductance d2 mounted within the shield can 48, and an adjustablyfixed capacitance coupling 31'. The corresponding elements for the several bands are similarly designated, except that each has a suffix representing the band for which such element is provided. In the -embodiment'of the invention illustrated, the receiver is tunable over four succesbands the coupling system functions in a manner similar to that described in detail for band a.

In this connection, it is to be observed that the Y is dependent upon the band under consideratiom ior the capacitance to groundof the primary circuit connections and the distributed capacitance of the shielded primary circuit inductances for the several bands vary to some extent.

Switch 21 in the primary circuits selectively connects in the outputi circuit of vacuum tube I4 the primary circuit 35 for the band to which the receiver is adjusted for reception. Similarly, switch 29 in the secondary circuits selectively connects in circuit with the input of the oscillator modulator l1 thesecondary circuit 38 for the band to which the receiver is adjusted for reception. Switch 28 in the primary circuits selectively short-circuits the primary circuit inductances for all bands below that to which the receiver' is adjusted for reception. Similarly, switch 30 in the secondary circuits selectively short-circuits the secondary circuit inductances lfor all bands below that'to which the receiver is adjusted for couplings 31 of progressively larger value as the bands over which the, receiver is tunable are higher in the frequency spectrum. 'This results in coupling system I8 having a progressively greater energy transfer in the higher frequency bandsthan in the lo\wer frequency bands, for, as j previously explained, the available over-all gain from antenna to detector in the high-frequency bands is, customarily, less` than that in the lowfrequency bands. i y

By virtue of such proportioning of the coupling capacitances 31, the bands in which the receiver is tunable are so determined that the ratios of thev maximum to minimum frequencies of the several bands progressively decrease as the bands are higher -in the frequency spectrum.

While I have described what I `at present consider the preferred embodiment of my invention, it will be obvious to those smlled in the art that various changes and modifications may be made therein without departing from my invention, and

I, therefore, aim in the appended claims to cover all such changes and modications asfall within the true spirit andscope of my invention.

What is claimed is: y

1. In a radio 4receiver including a plurality of vacuum tubes and a. circuit tunable'l over a given band of frequencies, a couplingsystem for coupling said tubes in cascade comprising; a primary circuit; a secondary circuit in non-inductive relation to said primary circuit and tunable over a band having a xed relationship to said given band; unicontrol means for simultaneously tuning said tunable circuits over their respective bands;and means for aligning said secondary circuit with said first tunablecircuit over said bandcomprising capacitance connected between said primary and secondary circuits.

2. In a radio receiver including a. plurality o vacuum tubes and a circuit tunable over a given band of frequencies, a coupling system for coupling said tubes in cascade comprising; a primary circuit xedly tuned to a frequency outside said given band; a secondary circuit in non-inductive relation to said primary circuit and tunable over a band having a fixed relationship to said given band; unicontrol means for simultaneously tuning said tunable circuits over their respective bands; and means for aligning said secondary circuit with said first tunable circuit comprising capacitance connected between said primary and secondary circuits.

3. Ina radio receiver tunable over-a givenband of frequencies and including a plurality of vacuum tubes; a first circuit, iixedly tuned to a fre-l quency 'below said given band, connected to the output of one of said tubes and having a portion thereof effectively grounded; a,` second circuit,

tunable over said given band and non-'inductively 4. In a radio receiver tunable over a given band,

of frequencies and including a plurality of vacuum tubes; a first circuit, iixedly tuned to a frequency below said given band, connected to the output of one. of. said tubesna second circuit,

tunable over said given band and non-inductively .f

related to said^ first circuit, connected to the input of a succeeding -one of said tubes; athird circuit tunable over s'aid given band; andmeans for aligning said second circuitl with said third lectively connecting said secondary circuits to 60 the output of said coupling system; and a cay. able over t'wo or more bands of frequencies, comcircuit comprising capacitance connected between said first circuit and said second circuit.

5. In a radio receiver tunable over a given band voi' frequencies and including a plurality of vacuum tubes; a first circuit,'flxedly tuned to a frequency below said given band, connected to the prising capacitance coupling connected betweensaid first circuit and said second circuit.

6. In a radio receiver, a tunable system comprising; a-primary circuit including a high inductance winding, said primary circuit having an inherent capacitance to ground permanently tuning said circuit; a secondary circuit including a low inductance winding non-inductively related to said primary circuit and including also a variable tuning condenser, one terminal of which is grounded; and a small adjustably-flxed capacitance interconnecting the high potential portion of said primary circuit with the high potential portion of said secondary circuit, and proportioned to serve, in conjunction with said inherent capacitance effectively in series therewith, as parallel aligning capacitance Afor said variable tuning condenser.

- 7. A coupling system for a radio receiver tunable over two or-more bands of frequencies. comprising; a primary circuit for each of said bands; means for selectively connecting said primary circuits with the input of said coupling system; a secondary circuit for each of said bands noninductively related to its respective primary circuit, said secondary circuits beingv tunable over their respective bands; means selectively connecting said secondary circuits to the output of said coupling system; and a capacitance for eachu 8. A coupling system for a radioreceiver tuni able over two or more bands of frequencies, colnprising; Aa primary circuit for each of said bands Aiixedly tuned to'a frequency below its respective band; means for selectively connecting said primary circuits with the input of said coupling system; a secondary circuit for each of said bands non-inductively related toits respective primary circuit, said secondary circuits being tunable over their respective bands; means sepacitance foreach of said bands, each capacitance coupling highpotential portionsof the prilmaryand secondary circuits of the corresponding band, said capacitances being progressively larger as the respective bands are higherin the frequency spectrum.` y

9. A coupling system for a radio receiver tunprising; a primary circuit, including a high-inductance winding for each of said bands fixedly tuned to a frequency below its respective band; means for selectively connecting said primary circuits with the input of said coupling system a low inductance winding for each ofA said bands non-inductively related to the inductance of the respective primary circuit: a variable tuning condenser; means for selectively connecting said low inductance windings with the'output of said coupling system and with said variable tuning condenser to form a plurality of secondary circuits non-inductively related to said primary circuits and tunable over their respective bands; and a small fixed capacitance for each of said bands, capacitively coupling the high potential terminal of the primary circuit inductance with a, high potential portion of the secondary circuit inductance for the respective bands, said capacitances being progressively larger as the respective bands are higher in the frequency spectrum.

10. In a multi-band radio receiver in which the ratios of the maximum to minimum frequencies in the several bands decrease as the bandsare respective bands are higher in the frequency spectrum; means for selectively connecting said primary circuits with the input of` said coupling system; a low inductance winding for each of said bands non-inductively related to the inductance of the respective primary circuits, said inductances being of decreasing magnitude as the respective bands are higher in thefrequency spectrum; a variable tuning condenser; means for selectively connecting said low inductances with the output of Ysaid. coupling system and with said variable tuning condenser to form a plurality of secondary circuits non-inductively related to said primary circuits and. tunable over their respective bands; and a small ilxed capacitance for each of said bands, capacitively couplingthe primary and secondary circuits forV the respective bands, said capacitances being progressively larger as the respective bands are' higher in the frequency 1l. In a multi-band radio receiver, a first tunable system selectively tunable over two or more frequency bands and a second tunable system selectivelyA tunable over bands having a fixed relationship with-respect to corresponding ones of said first-mentioned banda,v said first tunable system comprising; a plurality of primary circuits,'one for each of said mst-mentioned bands;

means for selectively connecting said primary circuits with the input of said coupling system; a plurality of secondary circuits, one for each. of said first-mentioned bands, with each of said secondary circuits non-inductively related to said primary circuits, said secondary circuits 'being tunable over their respectivebands; means for selectively connecting said secondary circuits to the output of said -coupling system; and means for aligning said secondary circuits for the several first-mentioned bands in the first tunable system with the tunable circuits for the corresponding second-mentioned bands in the secnd tunable system, comprising a capacitance for eacht of said first-mentioned bands connected between said `primary and secondary circuits for the corresponding band.

12. In aradio receiver having two vacuum tubes in cascade and tunable over two or more bands of frequencies in'which the' ratios of the maximum to minimum frequencies in the several bands de crease as the bands are higher in the frequency spectrum, a first tunable systema servspedisco tem between two cascaded vacuum tubes and selectively tunable over said bands, and asecond tunable system, including a variable capacitance of relatively large maximum value, selectively tunable over bands having a iixed relationship with respect to corresponding ones of said first-mentioned bands, said rst tunable system comprising; a high. inductance winding for each of said first-mentioned bands, one terminal o! each of .said inductances being eiiectively grounded; means selectively connecting said high inductance windings to the plate of the first of said cascaded vacuum tubes to form input circuits for said rst tunable system permanently tuned A to frequencies below the minimum irequencies of the respective first-mentioned bands by the inherent capacitances of said primary circuits, a

low inductance winding -for each of said ilrstrnentioned bands non-inductively related to the primary circuit inductance of the corresponding band; a second variable capacitance similar to said first variable capacitance and actuated coniointly therewith and having one terminal thereof grounded; means selectively connectingsaid low inductance winding with said second variable capacitance to form closed secondary circuits, severally tunable over said first-mentioned bands;

and a small adjustably-flxed capacitance vfor each of said flrst-mentionedbands connecting 'the high potential terminal of the primary circuit inductance with the high potential terminal of the secondary circuit inductance ot the corresponding band, said adiustably-flxed capacitance being proportioned to serve, in conjunction with said inherent capacitances effectively in series therewith, as parallel 'aligning capacitances for said second variable capacitance so that the secl ondary circuits for the several mst-mentioned bands in the iirst tunable system may be aligned with the tunable circuits for the corresponding second-mentioned bands in the 4second tunable system, such proportioning also compensating for the decrease in the gain as the bands are higher in the frequencyspectrum.

- NELSON P. CASE. 

